A wireless LAN system is popularly used as a communication system of a mobile terminal because the wireless LAN system has outstanding features such as versatility, inexpensiveness, and high flexibility for a position where a wireless LAN terminal is set. In such communication system, when a wireless LAN terminal communicates by radio, there are two modes. One is an infrastructure mode where the wireless LAN terminal communicates with another wireless LAN terminal or a node at a wired system via a wireless LAN access point. The other is an ad hoc mode where wireless LAN terminals communicate with each other directly. Protocol of such communication connection and disconnection thereof is set by a communication standard (a series of IEEE 802.11).
In this communication standard, it is provided that when a wireless LAN access point disconnects a wireless LAN terminal during connection, a disconnection frame (that is, a deauthentication frame) be sent from the wireless LAN access point to the wireless LAN terminal. There is no need to wait a response from the wireless LAN terminal after this disconnection frame was sent from a wireless LAN access point. The wireless LAN access point ends a disconnection process at the time when the disconnection frame has been sent.
Concerning disconnection of wireless connection, Japanese Laid-open Patent Publication No. 2007-116258 (paragraphs 0080, 0081 and 0082) discloses that when a slave device wirelessly connected to a plurality of wireless system master devices moves from an area of a wireless system master device connected to the slave to an area of another wireless system master device, advance notice of disconnection is sent from the wireless system master device connected to the slave to another wireless system master device. If the slave device determines that radio field intensity of the wireless system master device in the area where the slave device has moved is the highest-intensity, communication with the wireless system master device therein is established, and communication with wireless system master devices other than that of the highest intensity is disconnected.
Japanese Laid-open Patent Publication No. 2005-117488 (paragraphs 0017 and 0031, and FIGS. 1 and 2) discloses that an access point is a communication line (or a communication apparatus) used in order that a display and an intercom display and notify notice of communication disconnection, a password, etc. to a client in a specific area while a control unit monitors authentication of a client and time for communication connection, and controls connection with a client. Notice of password change is sent from the control unit of the access point to a client, and it is notified that the line is disconnected if this change order is not obeyed.
Japanese Laid-open Patent Publication No. 2005-287030 (Abstract, paragraphs 0004 and 0005, and FIG. 2) discloses that a request for dissociation is transmitted from a wireless local area network device of a host device to an access point of a wireless network to turn off a switch of a transceiver of the wireless LAN device.
In a disconnection process of wireless connection, a deauthentication frame sent from a wireless LAN access point is not encrypted. When this deauthentication frame is sent and received, a wireless LAN terminal does not authenticate a sending source. BSSID (Basic Service Set Identification) sent in disconnection is identification information for making a wireless LAN access point unique. BSSID is commonly a MAC (Media Access Control) address of a wireless interface of a wireless LAN access point. For this, if BSSID corresponds with a wireless LAN access point of a connection destination, a wireless LAN terminal accepts a deauthentication frame, and disconnects wireless LAN connection.
Since not encrypted, a deauthentication frame can be sent from another node easily. Since a sending source is not authenticated, wireless LAN connection can be easily disconnected by an irrelevant node of a third party. This means that disconnection by so-called “spoofing” can be easily performed. This prevents normal operation of a wireless LAN network.
Manufactures for security, which use the above reversely, exist. The manufactures send a dummy deauthentication frame to interrupt communication if a wireless LAN access point or a wireless LAN terminal, which are not allowed to be used, are detected.
For realizing normal wireless LAN operation, it is necessary to prevent disconnection by a deauthentication frame from a node of a third party.
Concerning such requests and problems, there is no disclosure nor suggestion thereof in any of Japanese Laid-open Patent Publication Nos. 2007-116258, 2005-117488 and 2005-287030, and no disclosure nor suggestion about structure, etc. solving them are presented.